1. Field of the Invention
This invention relates to a control system for a gas-turbine engine, more specifically a control system for a gas-turbine engine used in aircraft.
2. Description of the Related Art
A control system for a gas-turbine engine, particularly a gas-turbine engine used in aircraft, is generally equipped with at least two control channels, commonly referred to as the primary lane and secondary lane. The two control channels input the signals generated by a number of sensors provided in the respective channels for outputting values indicative of the turbine speed and other engine operating conditions. Based on the inputted values, they calculate a command value designating the amount of fuel to be supplied to the engine and perform self-diagnosis for determining presence/absence of malfunctions. When the primary lane does not make a fail self-diagnosis, the output of the command value calculated by the primary lane is outputted, while when the primary lane makes a fail self-diagnosis, the command value calculated by the secondary lane is outputted insofar as the secondary lane does not make a fail self-diagnosis. Fuel is supplied to the engine based on the outputted command value.
The command value in the two control channels is usually calculated from the sensor outputs using proportional and integral terms. Therefore, when the command value is immediately switched from that calculated by the primary lane to that calculated by the secondary lane, the newly implemented command value is liable to be inappropriate because the difference between the switched command value and the preceding command value becomes large due to the integral term.
To cope with this problem, U.S. Pat. No. 5,436,826 teaches a control system that includes dual fuel control having individual sensors that monitors N2 (high speed fan speed). Each control uses the average value of N2 from both sensors for providing fuel to the engine and performing other operations. The fuel controls contain signal processors capable of determining if their respective sensors are operating out of range, in which case the fuel control uses the value of N2 from sensors associated with the other fuel control. If both sensors are out of range, the signal processors use a stored value for N2 or a value synthesized from another engine parameter.
This prior art control system calculates the final command value from the outputs of the two controllers and does not rewrite the output of the primary lane with that of the secondary lane when the primary lane makes a fail self-diagnosis. The system therefore cannot overcome the problem that when the command value calculated by the primary lane is rewritten by that calculated by the secondary lane, the command value becomes inappropriate because the difference between it and the preceding command value becomes large.